Control of extracellular matrix remodeling by CD29+ astrocytes

PROJECT SUMMARY/ABSTRACT Remodeling of the extracellular matrix (ECM) is a central mechanism by which central nervous system (CNS) reward substrates, such as the nucleus accumbens (NAc), adapt to unpredictable stressors in the environment. The ECM is a spatially, molecularly, and cellularly heterogeneous structure that impacts neural activity, cell-cell

interactions, and blood-brain barrier integrity. However, exposure to repeated unpredictable stress leads to molecular and cellular reorganization of the ECM, which influences circuit-level adaptations to stress guiding neural activity and behavior. ECM remodeling is partially controlled by integrins: transmembrane receptors that

regulate the ECM by anchoring ECM-associated peptides to multiple cell types. Cellularly, the ECM consists of neuronal processes and also the endfeet of astrocytes, which are CNS-resident glial cells. Astrocytes make contacts throughout the ECM by expressing multiple integrins that actively participate in ECM remodeling.

Through these intimate interactions within the ECM, astrocytes are poised to control neural activity and behavior. However, the mechanisms and cell-cell interactions by which astrocytes shape the NAc ECM in response to unpredictable stress are largely unknown. In PREVIOUS RESEARCH EFFORTS I focused on characterizing

the responses of astrocyte subsets in the CNS in response to inflammation. I identified the b1 integrin CD29 as a top marker expressed by astrocytes throughout the CNS. CD29 participates in multiple complexes with other integrins that affect ECM organization. My previous data suggest that CD29+ astrocytes might be composed of

heterogeneous subsets that play complementary roles in remodeling the ECM by interacting with distinct cell types. However, it has been historically challenging to rapidly study the interactions of astrocyte subsets in vivo. To this end, I recently developed a new technique called RABID-seq that profiles astrocyte interactions with other

cells at high throughput, on the genome-wide scale, and with single-cell transcriptomic precision. Thus, RABID- seq is a candidate tool to define the interactions of CD29+ astrocyte subsets in the ECM in response to unpredictable stress. In this proposal, I AM PURSUING A NEW RESEARCH DIRECTION to identify how

exposure to unpredictable stress shapes CD29+ astrocyte interactions, localization, and function. I hypothesize that defined subsets of CD29+ astrocytes regulate distinct ECM domains that influence behavioral responses to unpredictable stress. I propose to test this hypothesis in the following Specific Aims. In Aim 1, I will define the

interactions of integrin-expressing CD29+ astrocyte subsets within the NAc in response to acute and chronic unpredictable stress using RABID-seq and CITE-seq. In Aim 2, I will spatially map the ECM domains occupied by each subset of CD29+ NAc astrocytes via spatial transcriptomics and CD29 cKO mice to uncover how CD29+

astrocytes remodel the ECM in response to stress. In Aim 3, I will define how CD29+ NAc astrocytes regulate the activity of parvalbumin+ interneurons in a reward-seeking paradigm after exposure to unpredictable stress. IN SUMMARY, I will study how stress affects the interactions, location, and function of NAc CD29+ astrocytes.